transformers

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101010

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Just got drawings 200 amp 480v 3 phase service for a 4- 8000 sq foot wharehouse complex.Minimal load for each space at this time.About a 11kw load.All gas heating and water heaters. No kitchens at this point.The engineer is calling for 15 kva transformers to feed each warehouse.Then calling for a 200 amp main lug panel( 120 /208) in each space. The transformers will be right next to the 200 amp panels .My question if properly protected on the primary side is this a violation?They have#12's on 25 amp breakers for the primary protection??? what is the smallest wire i can use on the load side?They have # 10"s.Everthing seems to be way undersized.Also would you not need secondary protection?Some times i miss somthing when it commes to transformer sizing
 
Almost okay.

1) Panel protection - This will be a lighting and appliance branch circuit panel per 408.34. It will need some type of main device per 408.36

2) Transformer protection - with a main lug only on the secondary the pimary protection can not exceed 22.5A (18 FLA * 125%) per 450.3(B).


A solution is to use #8 wire between the transformer and a backfeed 50A breaker in the panel.
 
I don't think your installation meets the requirements of 240.21.C(1) to allow primary protection for secondary conductors.
 
jim dungar said:
Almost okay.



2) Transformer protection - with a main lug only on the secondary the pimary protection can not exceed 22.5A (18 FLA * 125%) per 450.3(B).


Jim....How did you arrive at the 18FLA ?
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A solution is to use #8 wire between the transformer and a backfeed 50A breaker in the panel.[/quote]


Jim....If an OCPD was placed on the secondary side of the transformer could we use a 50A OCPD on the primary and a 60A on the secondary per 450.3 (B)?
 
101010 said:
Doesnt this seem small for a 8000 sq ft wharehouse?
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42:

Well the NEC only requires 1/4 VA/sq ft for lighting. And everything over 12.5KVA get's a 50% demand factor applied. I don't know what other loads you have, but it seems to meet code.

Steve
 
Is there a general rule for tranformers ?like 45 kva for 100amps 120/208 ,30 kva ....etc. Max amp for secondary side of step down trans for a certain kva?
 
m73214

Yes, you could use a larger primary breaker, but then you are really changing the project design.
 
the other question i dont see it there otherwise i might overlook on this one did you figures the lumiaires load ??

if my memory serve me right but i might be wrong on this one so please do correct me on this one there are few classfication of warehouse spacing useation [ sp ] so the lighting load can change pretty fast there


Merci , Marc
 
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